Final answer:
A cloud must contain lightning and thunder to be considered a thunderstorm, making the statement false as specific rain, cloud types, or hail sizes are variable conditions and not essential for defining a thunderstorm.
Step-by-step explanation:
A thunderstorm is scientifically defined as a local storm, invariably produced by a cumulonimbus cloud, and always accompanied by lightning and thunder, often with strong gusts of wind, heavy rain, and sometimes with hail. The presence of cumulus clouds with heavy rain or hail of a certain size alone does not qualify the cloud as a thunderstorm.
Therefore, the correct answer to whether a cloud must contain 'thunder and lightning, rain and dark clouds, cumulus clouds accompanied by heavy rain, hail of diameter 0.75 inches or more' to be considered a thunderstorm is False. Thunder and lightning are essential, but the other conditions can vary.